Logging shales



United States Patent LOGGING SHALES Donald C. Bond, Crystal Lake, 11]., assignor to The Pure .Oil Company, Chicago, 11]., a corporation of Ohio I No Drawing. Application August 2, 1951,

Serial N0. 240,058

4 Claims. C1. 23-230 This invention relates to a method of logging wells and particularly to a method of producing a well log by plotting the cation exchange properties of the clay content of the subsurface strata against the depth at 'which the particular formation is found.

In the constant search for petroleum bearing formations and optimum means for extracting the petroleum content of these formations, it is essential that as much information as possible concerning the nature of the strata lying beneath the surface of the earth be available. One of the most important problems confronting the subsurface engineer is the necessity of determining the same geological formation in each of several wells. In order to thus correlate these geological formations from :well to well, accurate data delineating one formation from another and recognizing the same formation in the wells, regardless of extraneous conditions, must be available. Of perhaps equal importance is the problem of determining whether the area in which an exploratory well is being drilled is a productive one and, if it is, whether the well is properly located. This problem can often be solved by a study of the characteristics of the formations traversed by a bore hole, thus eliminating unnecessary drilling in areas devoid of petroliferous formations. .In addition, in areas where water-drive is contemplated as a secondary recovery method it is desirable to know the nature of the formation to be flooded in order to obtain optimum results from the operation.

'Knowledgeof the nature of a particular formation is the depth at which the formation having the particular property selected is located. However, there is much valuable information regarding the nature of the sub- .surface formations which known methods of logging do not supply, the results obtained, by these methods are often obscured by extraneous conditions brought into -play by the methods of drilling utilized, and the data produced by conventional logging is often indistinct and incapable of accurate interpretation even by the most proficient observer.

It is accordingly an object of this inyention to provide a method of logging bore holes which can be used to correlate strata among a number of related wells;

A further object of this. invention is ,to provide a method of logging bore holes which will effectively recognize the same strata in a series of wells.

Afurther object of this invention is to provide a method of logging bore holes which will effectively recognize the same strata in a series of wells regardless of 2 the conditions of environment surrounding the formation in each well.

It is afurther object of this invention to provide a niethod'of logging bore holes which is uneffected'by the conditions under which the well is being drilled.

A further object of this invention is to provide a method of logging bore holes which is unetfected by the drilling fluid being used in the drilling operation.

A still further object of this invention is to provide a method of logging bore holes which is unetfected by the degree of drilling fluid flushing employed in the drilling operation.

A further object of this invention is to provide a method of logging bore holes which is highly sensitive to changes in subsurface formations.

Astill further object of this invention is to provide a method of logging bore holes which will clearly distinguishone formation from another.

Another and further object of this invention is to provide a method of logging bore holes which will supply information concerning the strata traversed by a bore hole which has not been available heretofore.

Another object of this invention is to provide a method of logging bore holes which will supply information concerning the history of the formations traversed by a bore hole. 7

Still another object of this invention is to provide a method of logging bore holes which will supply information concerning the conditions under which a shale was laid down. r

It is another object of this invention to provide a method of logging bore holes which will supply information concerning the environment in which a subsurface strata was laid down.

Another object of this invention is to provide a method of logging bore holes which will supply information regardingthe effect which a proposed reservoir. treatment will haveupon a formation to be treated.

of logging bore holes which will supply information re- Another object of this invention is to provide a method garding the effect which a water flooding operation will have on theformation flooded.

Still another object of this invention is to provide a method of logging bore holes which will supply information regarding the eifect which a well acidizing treatment, will have on the formation treated.

Other and further objects of this invention will be apparent from the following description of my invention.

In accordance with my invention it has been found that the above objects can be accomplished by collecting samples of the subsurface strata forming the wallsof a bore hole, determining the cation exchange properties of these samples, andcorrelating these values with the depth from which each sample was obtained to produce ,a log of the well.

The cation exchange properties of the clay content of an earth sample, adverted-rto here, include cation exchange capacity and concentration of exchangeable cations.

Cation. exchange capacity, as used in this specification and the appended claims, denotes that capacity of a clay 'materialvwhich enables the clay to give up certain posa given clay and clistinguish'it'from another clay having a a fi era it xc an e q pa ty- .A i an ea ure. of e. at nsx a sc ,s a y vQ w it istt a t s pe y Qa b t-c an d o y f t ay i .st bis t d to ath r. ve s titl ha 14 .11. 5 P o leas h at w th. s ens a d, lot ro h nt s tion. This pointis important in pr ducing a lo of a well bore due to the fa w i face water-hast: drilling fluid is l'zed there is a strong possibility tanni j anipie. of ra ta "tofb e exg ained, i h in ad slby W t a e i lt e 1311- ;.9ha sina-f iat bf saw l l f li is i vasion of the strata sample, w ll not ,i" rf lere with measureme nts ofthe exchange capacityof thesariijgile This "as. a ,v la.

" of exchanging 'atidns 'with'the clay,[such' as the [ability oi a lime-base fluid to exchangecalciium for sodium ade o r h ay h? mak n atio dorhedbutnot theftot al cation exchange capacityof y p e, t 'ad t n a c ayv of i i fv i n sitionmightbefl d c 'iwn'ov'efa given areafollowed by "in aii n tPitgfth rea la -Wa er t ic' n c f capable of replatjing "the": adsorhed ions on the" clay, for

, example,"calciu'm for sodium, I invasionjofthe clay Wquld h n e k s Q v a ha abl atio s ad or on the clay but would hange fiits cation exch'ange capacity, Th'erforefby easur'ing the'cation exchange "capacity 'of clay sample om"wells drillei'in both the invaded and uninvadedarasythis clay which fiscommon 5 to both -areas, would be recognized ascontempt)rary. I -"2acl-ayYdep6sited over a considerable area "duringa 1 'en 'p'erio d' 'of sedimentation wilPhave' the same cation 7 exchange capacity throughout th whole area. By pro- "ducinga log 'ofjthecation'exchange capacity of the' strata "traversed by fbd re hole-a Patternt haf should be duplicated in heighbor'ihg wellsiesults, 1 and the" strata may thus be cbr'relate'doiler theaiea.

It may be seen from the above thatthe m ethod of Q logging comprisihg my invention "will permit correlation "of sti ata ffr I ell towell regardless of the drilling fluid used-, invasion Of the area by Water, 1 or dthl extraneous conditions.

pmu ch valuable iinformation concerning the histc iry of the forrnation a n d the environment in which 'the formation "invention; thei'electrical 10gand other known 'meth'ods of *loggingmakej little distinction between one shale and "another. For example; an" electrical log"mayshow"the 's'arne electiicalspecific resistivity fortwo eritirely differ- *e'nt subsurface formations, andithel'og isoften'influenced by 'the: character jot the drilling fluid "used and t the thick- "n'ess of thefilmof drilling fl'uid onthe w'all'of the bore hole. Methods of log gingehiploying chemical analysis iire 'a'ls0 sub ct'to serious; disadvantages. *For'iexample, *ela' s ot'ide'ntieaPcliemical composition mawhave aiaerent cation exchange capacities and clays 0f"the%aine 'the'p dium in a formation sample will indicate that-a petroleum 1 bea g fe hmian will he located either ahovefbelow, or lat rallyhisplaeed from the point 'at which 'the sample cation exchange capacity may have difierent chemical compositions.

If an earth sample were merely analyzed for its content of a given cation, such as calcium, this analysis would result in an erroneous conclusion as to the type of formation present. This analysis for calcium would be influenced by the type of drilling'fluid used in the well or by the invasion of the area'by a water containing calcium or other compounds containing exchangeable cations. For examplega lime-basefniud'fwoulcl' exchange calcium for sodium oftheclay sample"and would*thus result in a high concentration of calcium cation which was not present inthe originalsa'ihple. Likewise, the invasion of the formation by aealciurn containing water would also exchange calcium ions for'sodium and thus alter the characteristics of the earth sample. From this it follows that a chemical analysis of an earth sample wouldbe in'fluenced by the type ,of mud used in drilling, by the degree of'dril ling fluid flushing, or by the invasion of the area by water containing calcium compounds. The analysis of the earth sample for cation exchange capacity would befinfluenced by none of these extraneous conditions, and this'method wouldrecognize a clay laid down during a given period of sedimentation as being co t porane us re rdl o e w di fim Surroun ingthe drilling vof the well or the environmental changes occurring after theiclay was laid down h h additional advantage of the 'deter mination of the type of clay present. At the same time, the

SiQz/RzQsfWhere R represents Al or a complex mixt ure of Al and ivlg ,iK, or other metals) ratio of the clay could vary o rilysthrough the range of about lzl up to 4:1. Thus 'the cation exchange capacity of 'a clay is a very sensitive indicator of differences in types of clays.

[ e li ete t at enf at th a em a, b @93 able cations on an earth sample enables vone to obtain was laiddown. "clay deposited in one environment will contain different absorbed cations than a clay laid down'in another; environment. For ex mples clay deposited in a fresh,'hard water environment will have calcium'asthe predominating absorbed cation. on the i'oth'erjhand, a clay depositedin' a strong brine environmene'wiu containsodiu'mas 'its predominafi i cation.

Also, ifstrOntium is present in thefwater'in whicha clay 'se'tt'lesist'rhntium will befoundadsorbed on the'fclay.

i By deteriiiniing the concentration "of exchangeable cations in an "earth s'ample'it i's't'hus possible'tonse'one of these exchan'geable cations" as a marker; to follow the particular formation over the steam; question. I Since the niarlger f-seie'cted; iich' as strontiumflwillbe"widely ageniforml distributed over a given"area,j'aiv'aluahle'mcans'rmr 'eo'rre lating formations in' a s'eri'es'of related'ivells' is p'rod z Infa ditienfto'theivalileioi a 10g of exchangeahle cat- 2 ions 'for correlation 'pur'po's'es; 'th e logs' will also-be of l v i :ue'in investigations of'the 'substrataf infame'xploratory i i l-s law egiih If ib t e'ip iafee 99" formations laid W wn 'inf a brine "environment, e ser iee bf'a hi'gh' concentratiomofexchangeable sof a am l r '"The adsorbed ions' onan 'e'ai'th sample also-give valuable ih formati'ori concerniiig 'th'e historyof the shale. For

example, passage'of water from an organic reef; contain- I ing strontium; 'th lf ou'g'h 'th'e shale would result inithe ad ;;sorptionnethe strontium by'the"shale. Therefore,: the

preseiiceiof'sti'bntilim in the shale asan absorbed cation shouldrindicatethe presence. of am'organiereefne'ar the shale'iro'mwhich 'the' sample was'extracted. v

--c1sy= minerals are found in t sands and sandstones" as discrete particlesmixed withthequartz grains and as a film 'plastered around the quartzgrainsw Due to the crystalline structureof theclay, structural changes often oc'cur when waterris passed through the clay." For -ex ample, if a: sand contains smallz amount's of inont'moril lonite; clay having calcium present as the predominating exchangeablecation. the passage of 'water containing sodium through the sand would cause the sodium to replace calciumin the clay; The result.-of:thisexchange wouldbe: the separationof the individual fiakes, asplit ting of :discrete clay particles, and au'uilplaste'ring of the quartz-grains- :The'netresult would bethe liberation of minutelclayimineral particles anda plugging of the sand by these particles; On-theo'therhand, if themontmorillonite ,carriedsodiumfas the predominating exchangeable iOD;3theIe WOuld "3321511116 or-no'cexchan'ge of cations and little: clogging; Therefore, if awater flooding operation is contemplated, it would be desirable to know the char acter of any clay component in the sand and the nature and concentration of exchangeable"cations inithe clay in order to determine the type of water touse for flooding or to select proper methods of pretreating a water to be used} A log of the exchangeable cation concentrationof such-a well would thus furnish the information necessary for'bbtaining optimum results from a; proposed flooding operation. 7 p The structuralchanges in'the character of a clay are not confined toc'hangesbroughtabout' by contact with waters containing various compounds. Certain structural changes 'occur when an acid solutionilsuchas hydrogen chloride, contacts aformation containing aclay. Clays existing in a productivedimestonei orfdolornite formation may occur enclosed by the limestone or dole mite or in' fractures and new channas of the formation. Whenan acid solution, such as HCl, contacts "such. aforiiiation thehydrogen of :the HCl will replace cations adsorbed on the clay. This' exchange of cations results in'aflocculation or a decrease in volume of the cl'ay'p'ar ticles- However, as the HQl attacks the limestone forrnatibncalcium is liberated and as ifatfacksa dolomite formation calcium and magnesium are liberated. Concurrent with this liberation of calcium and magnesium the reaction of the acid on the formation also changes the pH of the acid solution and in turn the pH of the environment of the clay. As the pH of the environment of the clay is altered an exchange of calcium and magnesium for the hydrogen adsorbed on the clay takes place. The net results of this exchange of cations and the concomitant change in pH of the environment of the clay is to cause the clay to swell and thus tend to neutralize the increase in formation permeability brought about by the acidizing treatment. By studying the log of a borehole produced by the method of my invention the type of clay present and the amount of exchangeable cations present can be determined and a proper antiswelling agent may be selected for addition to the acidizing solution.

In the practice of my invention, samples of the substrata are collected at spaced intervals in the bore hole. These samples may be those secured with a conventional vertical core barrel or side coring device or they may be cuttings from the drill bit which are brought to the surface by the circulation of the drilling fluid. The methods of determining the depth from which these samples are 7 collected are also well known in the art and form no part ion found in the solution subtracted tfromfithe NH ion content of an equal volume of the original NH4l solution is equal to the cation exchange capacity of the sample. This measurement of the amount of exchange ableeatiorls replaced by NH; ion should clieck with the sum total of individual cations asdete'rmined byanalysis' of'the eflluent' from the leaching. If a sample contains calcium carbonate or other'soluble' or decomposable sub= stances-andthe concentration of exchangeable calcium is to be determined-{this procedure may be varied slightly to ccrrrect for the-'alcium 'dissolved by the leachingpre= cedure'from the calcium carbonate presentin the sample; This correction issobtained 15y determining theicalcium carbonatecontent ofthe sample before and after leach mg, and then subtracting from the calcium found in the effiuent from "the leaching; an amount of calcium equiva lent to' calciun'r carbonate dissolved. Other methods of determining the cation exchange" capacity and the concent'r'atio'n or individual exchangeable cations of the samplel may be carried out and thea-bove test is notto be considered alimitation upon the invention described herein.

After the. values of cat'ion exchange capacity and ex changeable cations have been obtained, as set forth above; a" log of the wellhisipfepared byplo'tting these values versus the depth from which each sample was obtained;

Suinn'iarily, it'can'be seen that .the log? prepared by the methddjo'f my invention may" be used for the correlation of; subsurface strata over a given area* by matching the strata having:- thesar'ne cation exchange capacity in" each of'severa'lwells or by following an individual-exchange able=;cation through the subsurface formation.

Th'e logproducedby' the'methodof my invention may also be used to determine the environment under which a given clay Was laid downa That is,- it ma -be determined whether at clay was laid dow'n'ingan-ordinary' fresh water environment or in a marine environment.

My method of logging also enables the subsurface engineer to obtain information concerning the history of subsurface formations. Clay laid down during a given period of sedimentation followed by the passage of water from an organic reef, containing strontium, through the shale would indicate the changes in environment which had taken place subsequent to the time the clay was laid down.

An additional use of the log prepared by the method of my invention is the determination of the characteristics of formations which are to be water-flooded. Knowing the concentration of exchangeable cations in the formation, the proper water to use in a flooding operation can be selected or a given water may be treated accordingly. Thus undesirable plugging of the flooded formaiton may be avoided.

Further, the method of logging of my invention can be used to determine the type of clay present and the character of the exchangeable cations of such clay as a preliminary to a proposed acidizing treatment. In view of the type of clay present and the exchangeable cations of the clay, as determined by a study of my well log, a proper acidizing solution may be selected and proper control of the environment in the formation can be maintained in order: to obtain optimum results from an acidizing treatment. 7

It will be apparent that no attempt has been made to describe all the possible types of formation sampling which may be practiced in carrying out my invention or all types of tests which may be employed in analyzing thosesamples. .It will be understoodthat my invention issnot -to,.1beflimited to a particluar. method of collecting samples: or'zanalyzing'these samples, but contemplates broadlylany procedureby which samples of subsurface strata are collected and tested to determine their cation exchange capacity and the concentration of exchangeable cations present and correlating these values .with depth to produceawell log. v r The nature and objects of my invention having been described and illustrated above, what is claimed as new and' useful and is desired to be. secured by Letters Patent is:

1. A geophysical well logging process for determining the; characteristics and position of clayey strata containing exchangeable cations in the clayey constitutents of the strata which comprises collecting samples of said clayey strata at spaced intervals along a bore hole, leaching each of. said samples with a. solution containing a replacing cation not present in the clayey constituents of the strata to produce from each sample an eflluent whereby all of the exchangeable cations in each of said samples are-substantially completely replaced by said replacing cation and are contained in said. efiluent, thereafter determining the amount of replacing cation which is adsorbed by each of said samples whereby the total cation exchange capacity of each sample is ascertained, analyzing the efiluent from each sample to quantitatively and qualitatively identify at least one of. the exchangeable cations contained in 'each sample, and preparing a well log by correlating the total cation exchange capacity value of each sample and the determinations of the aforesaid qualitative and quantitative analysis of the eflluentfrom each sample with the position in the well bore from whichthe sample was obtained.

2 2. A process in accordance with claim 1 in which the replacing cation contained in said solution is NH4+.

3. A process in accordance with claim 1 in which the total cation exchange capacity is obtained by quantitatively analyzing saidefiluent for the amount of replacing cation derived from'said'solution contained therein whereby the total cation exchange capacity of each sample may be determined. i

4. A geophysical well logging process for determining the characteristics and position of clayey strata containing exchangeablecations in the clayeyconstituent'sfof. the strata which comprisesicollecting samples of said clayey strata-at spaced intervals along abore hole,'-comminuting each of said samples to produce. a..plura1ity .of samples each having substantially the same particle size, leaching' eachzof said samples with an ammonium chloride solution to'produce an efhuentfrom each of said samples whereby'all of the exchangeablecations in each sample are substantially completely replaced by theNHs cation contained in. said. solution and are contained in said effluent, determining the amount of NH4.+ cation adsorbed by each of said samples, whereby the total cation exchange capacity of eachsample is ascertained, quantitatively and qualitatively analyzing the eflluent from each" of said samples toldetermine the exchangeablecations contained therein and preparing a well'log by correlating the total cation exchange capacityvalue of-each sample, and the determinations of the aforesaid qualitative and quantitative analysis of the eflluent from each-sample withthe position in the wellbore from which the sample was obtained. I

. References Cited in the file of this patent UNITED STATES PATENTS 2,278,929 Horvitz Apr. 7, 1942 2,310,291 Horvitz Feb. 9,1943 2,336,613 Horvitz ...L;. Dec. 14, 1943 2,374,937 Horvitz May 1, 1945 U Horvitz May 14, 1946 V OTHER REFERENCES 7 1 Grim: Bull. AmfAssoc Petrol..Geol., vol. 31 1947 p .1491 1499.

: Geste'r: Bull; Am. Assoc. Petrol. Geol., vol. 31 (1947), pp. 375, 382, 383.; Hosking and Osmond: Jo. Council Sci. Ind. Research (l948),p.21. Y

Marshall andBergman: Jo. Phys. Chem., vol. 46 (1942), pp. 52, 60, 327, 333, 334.

Grim: World Oil,'.vol. 132,"No..4 (1951),ppf61, 62, 'Kautfman; World Oil, vol. 128, No. 3 (1948), pp. 1l8,120,124,'126.' 

4. A GEOPHYSICAL WELL LOGGING PROCESS FOR DETERMINING THE CHARACTERISTICS AND POSITION OF CLAYEY STRATA CONTAINING EXCHANGEABLE CATIONS IN THE CLAYEY CONSTITUENTS OF THE STRATA WHICH COMPRISES COLLECTING SAMPLES OF SAID CLAYEY STRATA AT SPACED INTERVALS ALONG A BORE HOLE, COMMINUTING EACH OF SAID SAMPLES TO PRODUCE A PLURALITY OF SAMPLES EACH HAVING SUBSTANTIALLY THE SAME PARTICLE SIZE, LEACHING EACH OF SAID SAMPLES WITH AN AMMONIUM CHLORIDE SOLUTION OT PRODUCE AN EFFLUENT FROM EACH OF SAID SAMPLES WHEREBY ALL OF THE EXCHANGEABLE CATIONS IN EACH SAPLE ARE SUBSTANTIALLY COMPLETELY REPLACED BY THE NH4+ CATION CONTAINED IN SAID SOLUTION AND ARE CONTAINED IN SAID EFFLUENT, DETERMINING THE AMOUNT OF NH4+ CATION ADSORBED BY EACH OF SAID SAMPLES, WHEREBY THE TOTAL CATION EXCHANGE CAPACITY OF EACH SAMPLE IS ASCERTAINED, QUANTITATIVELY AND QUALITATIVELY ANALYZING THE EFFLUENT FROM EACH OF SAID SAMPLES TO DETERMINE THE EXCHANGEABLE CATIONS CONTAINED THEREIN AND PREPARING A WELL LOG BY CORRELATING THE TOTAL CATION EXCHANGE CAPACITY VALUE OF EACH SAMPLE, AND THE DETERMINATIONS OF THE AFORESAID QUALITATIVE AND QUANTITATIVE ANALYSIS OF THE EFFLUENT FROM EACH SAMPLE WITH THE POSITION IN THE WELL BORE FROM WHICH THE SAMPLE WAS OBTAINED. 